In some machines, components are required to be maintained in a cryogenically cold temperature range in order to operate properly. For example, superconducting components of superconducting electrical machines are required to be maintained at a temperature where they exhibit superconductivity. In order to maintain a component in a cryogenic temperature range it is necessary to both cool the component and to insulate the component from adjacent components that are not maintained in the same temperature range. Even if a cryogenic component is contained within a vacuum chamber, in order to minimise heating of the component, it is generally necessary to further insulate the component in order to prevent radiation heat loads warming the component.
Conventionally, cryogenic components are insulated by wrapping the component in multi-layer insulation. This insulation is made of alternating thin sheets of aluminised biaxially-oriented polyethylene terephthalate (e.g. Mylar®, as manufactured by Dupont Teijin Films U.S. of Wilmington, Del.) and polyester net. Multi-layer insulation is necessarily very light and delicate.
For many static cryogenic components it is sufficient for the multi-layer insulation to be wrapped around the component and held in position with cryogenic tape. However, for cryogenic components that are not static but move during operation then the multi-layer insulation can fatigue during operation of the component and can even tear or delaminate. This can result in a severe reduction in the insulating efficiency of the multi-layer insulation. This effect is particularly pronounced for cryogenic components that rotate during operation and which are subject to large centripetal forces. An example of such cryogenic components would be those found in high-speed superconducting rotating electrical machines.
In light of the above, there is a need for improved insulation for cryogenic components that provides improved resistance to forces resulting from motion of the cryogenic component during operation. In particular, there is a need for improved insulation for the cryogenic components of high-speed superconducting rotating electrical machines.